1. Field of the Invention
The present invention relates to a method and apparatus for separating a higher vapor pressure component and/or particulate matter from a lower vapor pressure component in a fluid mixture. For example, a method and apparatus for separating a gas from a liquid. The functional portion of the apparatus is fitted to the inside of a pipeline so the separation can be made while the mixture is traveling through a pipeline. The method comprises contacting the mixture with an immiscible or low solubility stripping substance different from the high vapor pressure component and/or the particulate matter to be removed from the mixture. The higher vapor pressure component is extracted from the lower vapor pressure component of the mixture into the stripping substance. Any particulate matter removed must adhere either to the higher vapor pressure component or to the stripping substance. The stripping substance is then separated from the mixture, reducing the amount of high vapor pressure component and/or particulate matter in the mixture.
2. Background of the Invention
The removal of gas dissolved or held in suspension in a liquid by contacting the liquid with a stripping gas is known in the art. The requirement for removal of the dissolved gas is that the partial pressure of the dissolved gas in the stripping gas be lower than the partial pressure of the dissolved gas in the liquid, thus permitting mass transfer of the dissolved gas from the liquid into the stripping gas. The rate of removal of the dissolved gas from the liquid is controlled by the rate of diffusion of the dissolved gas from the liquid into the stripping gas phase. The dissolved gas in the liquid reaches equilibrium with the dissolved gas in the stripping gas in time, after which no additional dissolved gas diffuses from the liquid. The conditions for equilibrium may be described by Henry's Law. A good description of typical equilibrium phenomenon and of the kinds of parameters involved was presented in the Proceedings of the 17th Congress of European Brewing Convention, pp. 245-58, 1979, in an article by J. Hoggan et al., entitled "A SIMPLE PRODUCTION SYSTEM FOR THE DEOXYGENATION OF WATER". This article describes a method of removing (stripping) dissolved oxygen from water using nitrogen gas as the stripping gas. United Kingdom Provisional Patent Specification No. 1,156,417 of Harold Davidge and Charles Sydney Gibbs, published June 25, 1969, describes a method of removing dissolved oxygen from liquids by bubbling through the liquid a gas having a lower partial pressure of oxygen than that of the liquid, which gas does not react chemically with the liquid. A sparging device is used to feed the stripping gas, nitrogen, into the liquid. The oxygen removal rate is substantially increased by causing turbulent flow of the liquid stream at a point downstream of the point of introduction of the nitrogen gas. Different devices capable of creating turbulence are described.
U.S. Pat. No. 4,639,340 to Garrett dated Jan. 27, 1987, discloses a method for dissolving gas in a liquid comprising pressurizing a stream of liquid, introducing the gas into the pressurized stream to form a gas-liquid mixture traveling at a velocity less than the velocity of sound in the liquid, accelerating the pressurized mixture stream to a supersonic velocity to create a first shockwave effective to reduce the size of the gas bubbles in the stream, thereby forming a dispersion of the gas under pressure in the liquid, reducing the velocity of the stream below sonic velocity, and transporting the pressurized stream to an outlet near which the velocity of the pressurized stream is accelerated to supersonic velocity once more to create a second shockwave prior to exit of the stream from the outlet.
There are numerous applications for stripping gases out of liquids, one of the most common being stripping oxygen from liquids. Typical examples, not intended to be limiting, follow. In enhanced oil recovery, sea water is injected directly into oil wells. It is necessary to remove dissolved oxygen from the sea water prior to its use to minimize corrosion. The de-oxygenated water typically has less than 0.1 to 1 ppm of dissolved oxygen. In most cases, the oxygen removal is effected by vacuum de-aeration or hydrocarbon stripping. U.S. Pat. No. 4,017,276 to Bloem, dated Apr. 12, 1977, discloses a method of stripping dissolved oxygen from sea water using a nitrogen stripping gas. Sea water is introduced into a stripping tower, and as the result of countercurrent contact between the nitrogen stripping gas and the sea water, oxygen concentrations as low as 7.5 to 12 ppm remain in the sea water after stripping. U.S. Pat. No. 4,612,021 to Palmer, dated Sept. 16, 1986, and United Kingdom Patent Application GB 2127711, dated Apr. 18, 1984, disclose methods of de-oxygenating seawater used in waterflood petroleum recovery. United Kingdom patent GB No. 1531537, issued Nov. 8, 1978, discloses a method of using nitrogen gas to remove dissolved oxygen from sea water. The nitrogen is placed into cocurrent flow with the sea water and then mixed into the sea water using an in-line static mixer; the mixture is subsequently fed into a cyclone separator.
De-oxygenation of boiler feed water has typically been carried out in thermal de-aerators by raising the temperature of the water with steam. A. Beevers, Process Engineering of London, Vol. 66, No. 8, p. 41, August 1985, in an article entitled "Cool Way to De-aerate", reported using nitrogen as a stripping gas to remove oxygen and carbon dioxide from boiler feed water. Japanese Pat. No. JP 60/183012 discloses a method for removing dissolved oxygen in boiler feed water by nitrogen stripping.
Japanese Pat. No. JP 56/121681 discloses a method of removing oxygen from the water in an open cooling system used in a tire plant. The cooling water is sparged with nitrogen at a nitrogen:water ratio of 6:1.
Japanese Pat. No. JP 59/154109 discloses a method of sparging industrial water with nitrogen to reduce the oxygen content of such water to less than 0.1 ppm dissolved oxygen.
Japanese Pat. No. JP 58/133885 describes a method of removing oxygen from process water by sparging with nitrogen at reduced pressure.
U.S. Pat. No. 3,132,013 to Kumamoto et al., dated May 5, 1964, describes a process for treating feed water, including the removal of oxygen from the water using a nitrogen stripping gas.
U.S. Pat. No 3,732,668 to Nichols, dated May 15, 1973, discloses a system to be inserted within aircraft fuel tanks, whereby dissolved oxygen is removed from the fuel.
U.S. Pat. No. 4,352,682 to Kemp, Jr. et al., dated Oct. 5, 1982, describes a de-oxygenating unit for removal of oxygen from water which is to be used to produce carbonated beverages.
U.S. Pat. No. 4,259,360 to Venetucci et al, dated Mar. 31, 1981 describes a method of reducing dissolved oxygen content of foodstuffs and of water used in beverage production by gas sparging with nitrogen.
Most of the art cited above demonstrates the stripping of a first gas from a liquid using a second stripping gas. The objective is to obtain maximum removal of the first gas while minimizing power consumption as well as consumption of the stripping gas. It is also possible to remove particulate contaminants from a liquid using a stripping gas. The particulates may adhere to the stripping gas itself or may adhere to a volatile component within the liquid which is removed from the liquid by the stripping gas.
Stripping gas consumption has been reduced by generation of better mixing between the stripping gas and the liquid. The improved mixing may increase the available surface area of the stripping gas, and improves distribution of the stripping gas throughout the liquid. Either of these actions increases mass transfer of volatile components and/or particulates from the liquid into the stripping gas. However, the increased mixing has been achieved by creating turbulence between the stripping gas and the liquid, by methods such as in-line static mixers and the use of mixing chambers containing insoluble reticulated material through which the stripping gas-liquid mixture must pass. Increased turbulence has been obtained at the cost of increased pressure drop across process lines and mixing chambers, necessitating higher operating pressures, which tend to force the first, dissolved gas back into the liquid and to increase power consumption.
It would be desirable to find a method of increasing the effective surface area of the stripping gas which does not generate significantly increased system operational pressures (with accompanying detriment to separation and increased power consumption costs).